import XCTest
class ObserverRealWorld: XCTestCase {
func test() {
let cartManager = CartManager()
let navigationBar = UINavigationBar()
let cartVC = CartViewController()
cartManager.add(subscriber: navigationBar)
cartManager.add(subscriber: cartVC)
let apple = Food(id: 111, name: "Apple", price: 10, calories: 20)
cartManager.add(product: apple)
let tShirt = Clothes(id: 222, name: "T-shirt", price: 200, size: "L")
cartManager.add(product: tShirt)
cartManager.remove(product: apple)
}
}
protocol CartSubscriber: CustomStringConvertible {
func accept(changed cart: [Product])
}
protocol Product {
var id: Int { get }
var name: String { get }
var price: Double { get }
func isEqual(to product: Product) -> Bool
}
extension Product {
func isEqual(to product: Product) -> Bool {
return id == product.id
}
}
struct Food: Product {
var id: Int
var name: String
var price: Double
var calories: Int
}
struct Clothes: Product {
var id: Int
var name: String
var price: Double
var size: String
}
class CartManager {
private lazy var cart = [Product]()
private lazy var subscribers = [CartSubscriber]()
func add(subscriber: CartSubscriber) {
print("CartManager: I'am adding a new subscriber: \(subscriber.description)")
subscribers.append(subscriber)
}
func add(product: Product) {
print("\nCartManager: I'am adding a new product: \(product.name)")
cart.append(product)
notifySubscribers()
}
func remove(subscriber filter: (CartSubscriber) -> (Bool)) {
guard let index = subscribers.firstIndex(where: filter) else { return }
subscribers.remove(at: index)
}
func remove(product: Product) {
guard let index = cart.firstIndex(where: { $0.isEqual(to: product) }) else { return }
print("\nCartManager: Product '\(product.name)' is removed from a cart")
cart.remove(at: index)
notifySubscribers()
}
private func notifySubscribers() {
subscribers.forEach({ $0.accept(changed: cart) })
}
}
extension UINavigationBar: CartSubscriber {
func accept(changed cart: [Product]) {
print("UINavigationBar: Updating an appearance of navigation items")
}
open override var description: String { return "UINavigationBar" }
}
class CartViewController: UIViewController, CartSubscriber {
func accept(changed cart: [Product]) {
print("CartViewController: Updating an appearance of a list view with products")
}
open override var description: String { return "CartViewController" }
}